The invention relates to a monitoring system for a conveying device for flat articles, especially wafers.
Wafers are thin disks of silicon, as they are used for the manufacture of integrated circuits, solar cells, etc. Such wafers must be handled extremely carefully in clean rooms, as they are transported, during the course of the manufacture of the integrated circuit, the solar cell, etc., from one processing step to a further processing step.
FIG. 3 shows a schematic view of an apparatus for carrying out various processing steps of a wafer.
Two racks 4,6 are disposed in a housing 2 that forms a supply or storage chamber; the racks have receptacles 8 (FIG. 5) that are disposed one above the other and in which can be accommodated disks 10.
Via a motor 11 and by means of a device that is not illustrated in detail, the housing 2 can be displaced back and forth on a stationary rail 12 in the direction of the double arrow 14, so that in one selected position, the one rack 4, and in the other selected position, the other rack 6, is located across from an opening 16 of a housing 18 that has further openings 20 to which the working chambers 22 are connected.
Disposed in a housing 18 is a robot 24 (FIG. 4) that is provided with a supporting arm 26 on which is disposed a carriage 28. The carriage 28 has an indentation 30, the base 32 of which is provided with vacuum slots 34 as well as capacitive proximity sensors 36.
To move the supporting arm 26, motors 38 and 40 are provided via which the supporting arm 26 is pivoted in a plane of movement that is perpendicular to a central axis of rotation of the robot 24, and via which the spacing of the supporting arm from the axis of rotation can be altered. The carriage 28 can be rigidly connected to the supporting arm 26, or can be displaceable on the carrying arm 26 via a non-illustrated further drive means.
FIG. 5 shows a perspective front view of the partially cut away or basically open toward the front housing 2, whereby two chambers are visible, of which only the left one is provided with the rack 4. The motor 10 serves for the back and forth movement of the housing 2 upon the rail 12. As can be seen, the housing 2 is not directly displaceable on the rail 12, but rather is disposed upon a frame element 42 that together with the housing 2 is displaceable along the rail 12. The housing 2 can be displaced in height relative to the frame element 42 via a servo-motor 44, in the direction of the double arrow 46, so that the individual receptacles 8, with the wafers 10 accommodated therein, though not illustrated in FIG. 5, can be positioned one after the other at the same height.
The construction and function of the previously described apparatus, various embodiments of which are offered in commerce by various firms, are known and will therefore not be described in detail.
The basic function is such that pursuant to FIG. 3, the robot 24, in a one time lined-up, horizontal plane, introduces the carriage 28 out of the opening 16 and into an oppositely disposed receptacle of the rack 4. With the aid of the servo motor 44, the rack 4 is then lowered slightly vertically until the proximity sensors 36 register the approach of a wafer 10 that is disposed upon a base of a receptacle 8. With a further lowering of the rack 4, the wafer 10 comes to rest upon the base 32 of the indentation 30, where it is held in place upon activation of the vacuum slots 34. The carriage 28 subsequently moves out of the rack 4 into the interior of the housing 18 and through a first one of the openings 20 into a first one of the working chambers 22, where it is deposited and processed. The wafer 10 is subsequently picked up by the carriage 28 and introduced into a next one of the working chambers, etc. until, after passing through the processing steps in the individual working chambers 22, the wafer is deposited by the carriage 28 in the right rack 6 of FIG. 3, whereby pursuant to FIG. 3 the housing 2 is moved toward the left. The carriage 28 is subsequently moved out of the rack 6, the housing is moved toward the right and the next wafer is picked up from the rack 4 by first lowering the rack by the height of one receptacle, so that after the carriage 28 has been introduced into the next receptacle, and after a subsequent further lowering of the rack 4, the next wafer 10 comes to rest on the carriage 28.
The individual openings 16 and 20 of the housing 18 can be sealed off via vacuum-type slides, so that on the whole it is possible to operate under vacuum.
A problem that arises when processing with the described apparatus is that the carriage 28 that is moved by the robot 24 alters its horizontal plane of movement, either due to wear or due to high thermal stresses as it is introduced into the working chambers 22, which are in part under high temperature. The vertical distance between the individual receptacles 18 in the racks 4 and 6 is relatively small, so that already a slight deformation or deflection of the carriage out of its targeted path of movement brings with it the danger that already upon its introduction into the rack 4 the carriage contacts a wafer and damages it, or that the wafer is then no longer satisfactorily deposited upon the carriage.
It is an object of the invention to provide a remedy for the aforementioned problem.
This object is realized by a monitoring system pursuant to the main claim.
The inventive monitoring system ensures that already slight deviations of the carriage movement from the targeted path of the carriage are detected and can be indicated. In this way, expensive damage to the wafers can be avoided.
It is to be understood that the inventive monitoring system for conveying devices pursuant to the main claim is suitable for many different types of flat articles, such as fragile, thin mica plates, thin ceramic plates, loaded printed circuit boards, etc. The inventive monitoring system is particularly well suited for conveying devices for wafers, the handling of which is subjected to particularly high requirements.
The dependent claims are directed to advantageous embodiments and further developments of the inventive monitoring system.